1. Field of the Invention
The present invention relates to monolithic electronic components and methods for manufacturing the monolithic electronic components. The present invention particularly relates to a monolithic electronic component including a laminate and external electrodes formed on the laminate by plating and a method for manufacturing the monolithic electronic component.
2. Description of the Related Art
As shown in FIG. 3, a monolithic electronic component 101, such as a monolithic capacitor, usually includes a laminate 102 including a plurality of stacked insulating layers 103 and a plurality of laminar internal electrodes 104 and 105 extending between the insulating layers 103. The internal electrodes 104 and 105 have end portions exposed at end surfaces 106 and 107 of the laminate 102. External electrodes are disposed on the end surfaces 106 and 107 of the laminate 102 such that the exposed end portions of the internal electrodes 104 are electrically connected to each other and the exposed end portions of the internal electrodes 105 are electrically connected to each other.
The external electrodes are usually formed as described below. A metal paste including a metal component and a glass component is applied to the end surfaces 106 and 107 of the laminate 102 and then baked, whereby paste electrode layers 108 and 109 are formed. First plating layers 110 and 111 made of, for example, nickel are formed on the paste electrode layers 108 and 109, respectively. Second plating layers 112 and 113 made of, for example, tin are formed on the first plating layers 110 and 111, respectively. Therefore, the external electrodes each have a three-layer structure including the paste electrode layers 108 and 109, the first plating layers 110 and 111, and the second plating layers 112 and 113.
Since the monolithic electronic component 101 is soldered onto a circuit board, the external electrodes need to have good solder wettability. Furthermore, the external electrodes need to electrically connect the internal electrodes 104 and 105, which are electrically insulated from each other, to each other. The second plating layers 112 and 113 have wettability to solder. The paste electrode layers 108 and 109 electrically connect the internal electrodes 104 and 105 to each other. The first plating layers 110 and 111 prevent solder erosion during soldering.
The paste electrode layers 108 and 109 have a thickness of several tens to several hundreds of micrometers. In order to limit the dimensions of the monolithic electronic component 101 to predetermined standard values, the effective volume necessary to ensure the capacitance undesirably must be reduced because the paste electrode layers 108 and 109 occupy a large volume. On the other hand, the second plating layers 112 and 113 have a thickness of several micrometers. Therefore, if the external electrodes include the second plating layers 112 and 113 only, the effective volume necessary to ensure the capacitance can be increased.
For example, Japanese Unexamined Patent Application Publication No. 63-169014 discloses a process in which conductive metal layers are formed over a corresponding one of side surfaces of a laminate by electroless plating such that internal electrodes exposed at the side surfaces thereof are short-circuited.
In the monolithic electronic component disclosed in Japanese Unexamined Patent Application Publication No. 63-169014, a laminate includes internal electrodes which are made of nickel and which are exposed at surfaces of this laminate. The surfaces thereof may be plated with various metals and may be directly plated with, for example, copper, which has good growing power.
The process disclosed in Japanese Unexamined Patent Application Publication No. 63-169014 has a problem in that some of the junctions between the internal electrodes, which are made of nickel, and copper plating layers, are broken by heat shock due to reflow soldering, and therefore, a reduction in capacitance is caused.